How can one complete his magrib salah when he joins the magrib jamat in last khaida?

Answer:

(Fatwa: 763/763=M/1430)

He will stand up after the imam turns his head for salam. Having recited sana, ta?awwuz and bismillah, he will recite Surah Fatihah with any other surah. Having completed one rak?ah with proper ruku and sajdah, he will stand up for second rak?ah. Just like first rak?ah, he will recite Surah Fatihah with any other surah and perform ruku and sajdah and sit for first qa?dah reciting Al-tahiyyaat. After Al-tahiyyaat, he will stand up for third rak?ah, recite Surah Fatihah and proceed to ruku and perform the salah in proper usual way.

Allah (Subhana Wa Ta’ala) knows Best

Darul Ifta,
Darul Uloom Deoband